US 7816873 B2 Abstract The present invention discloses an apparatus and method for controlling a linear compressor which can actively handle load and efficiently perform an operation, by synchronizing an operation frequency with a natural frequency of a movable member varied by the load. The apparatus for controlling the linear compressor includes a counter electromotive force phase detecting unit for detecting a phase of a counter electromotive force from a voltage command value of the linear compressor and an input current, a current phase detecting unit for detecting a phase of the input current, a frequency generating unit for comparing the phase of the counter electromotive force with the phase of the input current, and generating a frequency change value, a control unit for correcting the voltage command value according to the frequency change value, and an inverter unit for receiving a direct current voltage, generating a sine wave voltage according to the corrected voltage command value, and applying the sine wave voltage to the linear compressor.
Claims(8) 1. An apparatus for controlling a linear compressor, comprising:
a counter electromotive force phase detecting unit for detecting a phase of a counter electromotive force E from a voltage command value V* of the linear compressor, an input current i and electrical variables;
a current phase detecting unit for detecting a phase of the input current i;
a frequency generating unit for comparing the phase of the counter electromotive force E with the phase of the input current i, and generating a frequency change value;
a control unit for correcting the voltage command value V* according to the frequency change value; and
an inverter unit for receiving a direct current voltage, generating a sine wave voltage according to the corrected voltage command value V*, and applying the sine wave voltage to the linear compressor.
2. The apparatus of
(R: winding resistance, L: inductance).
3. The apparatus of
4. The apparatus of
5. A method for controlling a linear compressor, comprising the steps of:
detecting a phase of a counter electromotive force E from a voltage command value V* of the linear compressor, an input current i and electrical variables;
detecting a phase of the input current i;
comparing the phase of the counter electromotive force E with the phase of the input current i, and generating a frequency change value;
correcting the voltage command value V* according to the frequency change value; and
receiving a direct current voltage, and generating a sine wave voltage according to the corrected voltage command value V*.
6. The method of
(R: winding resistance, L: inductance).
7. The method of
8. The method of
Description The present invention relates to an apparatus and method for controlling a linear compressor which can actively handle load and efficiently perform an operation, by synchronizing an operation frequency with a natural frequency of a movable member varied by the load. In general, a compressor that is a mechanical apparatus for increasing a pressure, by receiving power from a power unit system such as an electric motor or turbine and compressing air, refrigerants or other various operation gases has been widely used for home appliances such as a refrigerator and an air conditioner or in the whole industrial fields. The compressors are roughly divided into a reciprocating compressor having a compression space through which operation gases are sucked or discharged between a piston and a cylinder, so that the piston can be linearly reciprocated inside the cylinder to compress refrigerants, a rotary compressor having a compression space through which operation gases are sucked or discharged between an eccentrically-rotated roller and a cylinder, so that the roller can be eccentrically rotated on the inner walls of the cylinder to compress refrigerants, and a scroll compressor having a compression space through which operation gases are sucked or discharged between an orbiting scroll and a fixed scroll, so that the orbiting scroll can be rotated with the fixed scroll to compress refrigerants. Recently, among the reciprocating compressors, a linear compressor has been mass-produced because it has high compression efficiency and simple structure by removing mechanical loss by motion conversion by directly connecting a piston to a driving motor performing linear reciprocation. Generally, the linear compressor which sucks, compresses and discharges refrigerants by using a linear driving force of the motor includes a compression unit consisting of a cylinder and a piston for compressing refrigerant gases, and a driving unit consisting of a linear motor for supplying a driving force to the compression unit. In detail, in the linear compressor, the cylinder is fixedly installed in a closed vessel, and the piston is installed in the cylinder to perform linear reciprocation. When the piston is linearly reciprocated inside the cylinder, refrigerants are sucked into a compression space in the cylinder, compressed and discharged. A suction valve assembly and a discharge valve assembly are installed in the compression space, for controlling suction and discharge of the refrigerants according to the inside pressure of the compression space. In addition, the linear motor for generating a linear motion force to the piston is installed to be connected to the piston. An inner stator and an outer stator formed by stacking a plurality of laminations at the periphery of the cylinder in the circumferential direction are installed on the linear motor with a predetermined gap. A coil is coiled inside the inner stator or the outer stator, and a permanent magnet is installed at the gap between the inner stator and the outer stator to be connected to the piston. Here, the permanent magnet is installed to be movable in the motion direction of the piston, and linearly reciprocated in the motion direction of the piston by an electromagnetic force generated when a current flows through the coil. Normally, the linear motor is operated at a constant operation frequency f On the other hand, various springs are installed to elastically support the piston in the motion direction even though the piston is linearly reciprocated by the linear motor. In detail, a coil spring which is a kind of mechanical spring is installed to be elastically supported by the closed vessel and the cylinder in the motion direction of the piston. Also, the refrigerants sucked into the compression space serve as a gas spring. The coil spring has a constant mechanical spring constant K The thusly-calculated natural frequency f Accordingly, in the linear compressor, when a current is applied to the linear motor, the current flows through the coil to generate an electromagnetic force by interactions with the outer stator and the inner stator, and the permanent magnet and the piston connected to the permanent magnet are linearly reciprocated by the electromagnetic force. Here, the linear motor is operated at the constant operation frequency f As described above, when the piston is linearly reciprocated inside the cylinder, the inside pressure of the compression space is changed. The refrigerants are sucked into the compression space, compressed and discharged according to changes of the inside pressure of the compression space. The linear compressor is formed to be operated at the operation frequency f However, since the actual load of the linear compressor is varied, the gas spring constant K In detail, as illustrated in
Here, f Generally, since the gas spring constant K However, the more the actual load increases, the more the pressure and temperature of the refrigerants in the restricted space increase. Accordingly, an elastic force of the gas spring itself increases, to increase the gas spring constant K Referring to However, the natural frequency f In addition, the natural frequency f As a result, in the conventional linear compressor, when the load is varied, the natural frequency f The present invention is achieved to solve the above problems. An object of the present invention is to provide an apparatus and method for controlling a linear compressor which enable the linear compressor to perform suction and compression in the resonance state, by synchronizing an operation frequency of a linear motor with a mechanical natural frequency. Another object of the present invention is to provide an apparatus and method for controlling a linear compressor which can overcome structural errors of the linear compressor, by estimating a mechanical natural frequency varied by load, and synchronizing an operation frequency with the mechanical natural frequency. In order to achieve the above-described objects of the invention, there is provided an apparatus for controlling a linear compressor, comprising: a counter electromotive force phase detecting unit for detecting a phase of a counter electromotive force E from a voltage command value V* of the linear compressor and an input current i, a current phase detecting unit for detecting a phase of the input current i, a frequency generating unit for comparing the phase of the counter electromotive force E with the phase of the input current i, and generating a frequency change value, a control unit for correcting the voltage command value V* according to the frequency change value, and an inverter unit for receiving a direct current voltage, generating a sine wave voltage according to the corrected voltage command value V*, and applying the sine wave voltage to the linear compressor. Preferably, the counter electromotive force phase detecting unit detects the phase by operating the counter electromotive force E by the following Formula:
(R: Winding Resistance, L: Inductance) Preferably, the frequency generating unit generates the frequency change value so that the phase of the counter electromotive force E and the phase of the input current i can be inphase. Preferably, the control unit transmits the corrected voltage command value V* to the inverter unit in the form of a predetermined inverter control signal. According to another aspect of the present invention, a method for controlling a linear compressor includes the steps of: detecting a phase of a counter electromotive force E from a voltage command value V* of the linear compressor and an input current i, detecting a phase of the input current i, comparing the phase of the counter electromotive force E with the phase of the input current i, and generating a frequency change value, correcting the voltage command value V* according to the frequency change value, and receiving a direct current voltage, and generating a sine wave voltage according to the corrected voltage command value V*. The present invention will become better understood with reference to the accompanying drawings which are given only by way of illustration and thus are not limitative of the present invention, wherein: A linear compressor in accordance with preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. As shown in In addition, a suction valve The top and bottom shells of the closed vessel The inside bottom surface of the closed vessel The cylinder The piston Here, the discharge valve assembly An indented loop pipe Therefore, when the piston A refrigerant passage The suction valve Accordingly, when the piston Especially, the piston Here, the mechanical springs However, the gas spring has a gas spring constant K While the mechanical spring constant K Even if the load is varied, the mechanical spring constant K The load can be measured in various ways. Since the linear compressor is installed in a refrigeration/air conditioning cycle for compressing, condensing, expanding and evaporating refrigerants, the load can be defined as a difference between a condensing pressure which is a pressure of condensing refrigerants and an evaporating pressure which is a pressure of evaporating refrigerants. In order to improve accuracy, the load is determined in consideration of an average pressure of the condensing pressure and the evaporating pressure. That is, the load is calculated in proportion to the difference between the condensing pressure and the evaporating pressure and the average pressure. The more the load increases, the higher the gas spring constant K As illustrated in The linear motor In the linear motor
Here, R represents an equivalent resistance, L represents an equivalent inductance coefficient, i represents a current flowing through the motor, and V* represents a voltage command value corresponding to an output voltage from an inverter unit (refer to In addition, the theoretical basis of the motion of the piston
Here, x represents a displacement of the piston
Here, ω represents an angular velocity (ω=2π·f The mechanical resonance occurs when the counter electromotive force and the current are inphase. Therefore, as known from the above Formula 4, in theory, the complex number part of the denominator must be zero. However, as described above, the equivalent spring constant k is obtained by adding up the mechanical spring constant K Referring to In detail, the counter electromotive force phase detecting unit The frequency generating unit The control unit Here, the control unit As discussed earlier, in accordance with the present invention, the apparatus and method for controlling the linear compressor achieve the resonance state by using the variables (R, L, i, V*) measurable in the electrical model, instead of estimating the natural frequency f The linear compressor in which the moving magnet type linear motor is operated and the piston connected to the linear motor is linearly reciprocated inside the cylinder to suck, compress and discharge the refrigerants has been explained in detail on the basis of the preferred embodiments and accompanying drawings. However, although the preferred embodiments of the present invention have been described, it is understood that the present invention should not be limited to these preferred embodiments but various changes and modifications can be made by one skilled in the art within the spirit and scope of the present invention as hereinafter claimed. Patent Citations
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